The invention concerns a method, a device and an apparatus for the surface treatment such as a cleaning operation and/or a covering operation for metal can bodies, preferably of Al or alloys thereof, more particularly can bodies which are produced by drawing, drawing and ironing or impact extrusion.
Before final filling such cans are generally prepared on their internal and/or external surfaces by means of cleaning treatments for removing the various pollutants resulting from the preceeding shaping operations (for example the residues of lubricants), and coating operations, generally using an organic material, in order to withstand subsequent physical or chemical attacks, both on the part of the content and the external environment.
A particular feature of the mode of manufacture of such cans is that they are formed at a high rate, of the order of 2000 cans per minute, which means that the cleaning and coating operations must be fast in order not to constitute a bottle-neck in their manufacture, whether the process is continuous (can-by-can) or discontinuous (in batches of cans).
The solution which is generally adopted in the prior art is treatment of each can individually and successively at a plurality of working stations, each being of very short duration, typically 1 second, and therefore involves an automatic system for fast transportation from one station to another, of the carousel type (see for example U.S. Pat. No. 3,969,136 or U.S. Pat. No. 4,883,578). In addition, as regards the organic coating which is generally deposited by electrophoresis, with the can constituting one of the electrodes, the counter-electrode or counter-electrodes must be disposed in the immediate vicinity of the surface of the can to be coated, which requires a specific device in relation to the size of can in question and thus involves multiplying the tools required, see for example GB-A-2 085 474 or U.S. Pat. No. 4,400,251.